1. Field of the Invention
The present invention relates generally to the field of electronic circuits and more specifically relates to systems and methods for generating frequencies.
2. Related Art
Oscillators are typically used to convert a DC input (the control current or voltage) into an AC output (the waveform), which can have a wide range of different wave shapes and frequencies that can be either complicated in nature or simple sine waves depending upon the application.
Oscillators are also used in many pieces of test equipment producing either sinusoidal sine waves, square, saw tooth or triangular shaped waveforms or even a train of pulses having a variable or constant width. An oscillator is basically an amplifier with “positive feedback,” or regenerative feedback (in-phase).
Voltage or current controlled oscillators are often used to generate frequencies in complementary metal-oxide-semiconductor (CMOS) circuits. The generated frequencies are used in synthesizers, communication, including radio frequency (RF) and digital, frequency multiplication, and other applications. In some cases, the frequencies are used as part of a phase-locked loop (PLL) or delay-locked loop (DLL) circuit. In all of these applications, the ability to tune an output frequency (and often the output phase) is typically provided.
Those skilled in the art will recognize that there are many types of oscillators used to generate frequencies including crystal oscillators, inductor-capacitor (LC) oscillators, Colpitts oscillators, Hartley oscillators, etc. Many voltage-controlled CMOS oscillators are implemented using a current starved inverter, single-ended amplifiers, or differential amplifiers.
All of these oscillators will generally have widely varying performance over the processing corners and temperature and all are generally dependent on the voltage amplification of the devices, which may vary with processing and with the ambient temperature. The number of stages varies from two to N for most oscillators and the oscillators will generally use a combination of phase shift and inversion of the stages to generate a frequency that is dependent upon the voltage gain in each separate stage.
While many presently known oscillators are suitable for certain applications, the dependencies associated with temperature variation and voltage amplification make it somewhat difficult to generate the appropriate frequencies for certain applications. Accordingly, without creating additional systems and methods for frequency generation over a wider range of ambient temperature and voltages, frequency generation will continue to be sub-optimal.